Effect of ocean oxidation on the chemical structure of marine kerogen

Longbottom, Todd L.; Hockaday, William C.; Boling, Kenneth S.; Dworkin, Steven I.

doi:10.1016/j.orggeochem.2017.01.002

Cited by 16 publications

(7 citation statements)

References 64 publications

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“…Numerous studies have focused on investigating molecular structure of kerogen. ,, Different kinds of techniques have been applied to study the molecular structure of kerogen, such as element analysis, solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. Great advances have been achieved in the characterization of kerogen chemical structure. ,− It has been proven that kerogens in different shales can be classified into three types according to origin and chemical structure . Types I and II kerogens have larger atomic H/C and atomic O/C ratios than type III kerogens, and with increasing maturity, H/C and O/C ratios in these three types of kerogens all decrease continuously .…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Spatial Alignment of Kerogen in Shale Using High-Resolution Transmission Electron Microscopy, Raman Spectroscopy, and Fourier Transform Infrared

et al. 2018

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As the three-dimensional (3D) molecular structure of kerogen plays important roles in further understanding of shale gas storage and transport, accurate characterization methods for 3D kerogen structures are attracting increasing attention. Spatial alignment is important information for 3D kerogen modeling, but was usually ignored in previous studies. In this work, seven kerogen samples with different maturities were isolated from organic-rich shale using a chemical method and highresolution transmission electron microscopy (HRTEM) was employed to quantitatively characterize the spatial alignment of these seven kerogen samples. Raman spectroscopy was used to investigate the overall structural disorder of the kerogen molecules and Fourier transform infrared (FT-IR) was conducted to study the chemical structure of these kerogen samples. The results show that immature, mature, and overmature kerogen samples all show an obvious alignment on the scale of 20 nm × 20 nm. In the immature kerogen sample Yl-1 with equivalent vitrinite reflectance (VR eqv ) = 0.4%, 60% of total aromatic fringes align in the major direction (with a 60°range), while 87% of the total aromatic fringes align in the major direction for the overmature kerogen sample Lmx-3 (VR eqv = 3.1%). However, unlike local alignment in the scale of 20 nm × 20 nm, the aromatic fringes in different regions may have different directions in larger scale. Meanwhile, based on FT-IR data, aliphatic carbons and oxygen containing functional groups contribute to a large proportion in immature, mature, and overmature kerogen samples. Thus, immature, mature and overmature kerogen samples all show overall disorder according to Raman data. In addition, the size of aromatic rings is also quantitatively characterized based on HRTEM images. In immature kerogen samples, the proportion of aromatic rings smaller than 3 × 3 is larger than 70%. In mature and overmature kerogen samples, 3 × 3 sized aromatic rings always occupy the largest proportion. This study provides the quantitative information on spatial alignment and the size of aromatic rings for kerogen samples, which contribute to an improved understanding of the 3D structure of kerogen.

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Section: Introductionmentioning

confidence: 99%

Evaluation of Spatial Alignment of Kerogen in Shale Using High-Resolution Transmission Electron Microscopy, Raman Spectroscopy, and Fourier Transform Infrared

et al. 2018

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“…NMR analysis was conducted with a standard bore 300 MHz Bruker Avance III spectrometer (Bruker BioSpin, Billerica, MA) equipped with a 4 mm magic angle spinning (MAS) probe, operating at a spinning frequency of 12,000 Hz, following the method by Longbottom et al (2017) . Spectra were acquired with a variable amplitude cross-polarization (CP) sequence with 1 ms contact time and composite pulse decoupling during signal acquisition.…”

Section: Methodsmentioning

confidence: 99%

Ferrate(VI) pretreatment before disinfection: An effective approach to controlling unsaturated and aromatic halo-disinfection byproducts in chlorinated and chloraminated drinking waters

Liu

Lujan

Dhungana

et al. 2020

Environment International

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Disinfection is an essential process of drinking water treatment to eliminate harmful pathogens, but it generates potentially toxic disinfection byproducts (DBPs). Ferrate (FeO 4 2- , Fe(VI)) was used to pre-oxidize natural organic matter (NOM, the precursor of DBPs) in source water to control DBP formation in subsequent chlorine or chloramine disinfection. Currently, it is unclear how Fe(VI) changes the structure of NOM, and no information details the effect of Fe(VI) pretreatment on the aromatic DBPs or the speciation of overall DBPs generated in subsequent disinfection of drinking water. In the present paper, Fe(VI) was applied to pretreat simulated source water samples at a Fe(VI) to dissolved organic carbon mole ratio of 1:1 at pH 8.0. 13 C nuclear magnetic resonance spectroscopy was newly employed to characterize NOM in simulated source waters with and without Fe(VI) treatment, and it was demonstrated that Fe(VI) converted unsaturated aromatic C functional groups in NOM to saturated aliphatic ones. High-resolution mass spectrometry (HRMS) and high performance liquid chromatography/triple quadrupole MS were applied to analyze the DBPs generated in chlorination and chloramination of the source waters with and without Fe(VI) pretreatment. It was confirmed that Fe(VI) pretreatment followed by chlorination (or chloramination), generated DBPs containing less unsaturated, halogenated, and aromatic moieties than chlorination (or chloramination) without pretreatment by Fe(VI). Finally, the cytotoxicity of disinfected drinking water samples were assessed with the human epithelial colorectal adenocarcinoma Caco-2 cell line (a model of the intestinal barrier for ingested toxicants), and the results show that Fe(VI) pretreatment detoxified the chlorinated and chloraminated drinking waters.

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“…When investigating the molecular structure of kerogen, different kinds of techniques are usually used, such as element analysis, solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy (Vandenbroucke and Largeau, 2007). Several kerogen structural models have been built based on the qualitative or semiquantitative information provided by these methods (Requejo et al, 1992;Orendt et al, 2013;Craddock et al, 2017;Hackley et al, 2017;Longbottom et al, 2017;Stock et al, 2017). In addition, these 3D kerogen models have been used in methane adsorption and micropore structure analysis (Huang et al, 2017).…”

Section: Molecular Structure Of Kerogen In the Longmaxi Shale: Insighmentioning

confidence: 99%

“…Great advances have been achieved in the characterization of kerogen chemical structure (Requejo et al, 1992;Vandenbroucke and Largeau, 2007;Longbottom et al, 2017). The evolution of the kerogen structure in shale has been the focus of previous studies (Vandenbroucke and Largeau, 2007).…”

mentioning

confidence: 99%

Molecular Structure of Kerogen in the Longmaxi Shale: Insights from Solid State NMR, FT‐IR, XRD and HRTEM

Wang

Zhu

Liu

et al. 2019

Acta Geologica Sinica (Eng)

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Kerogen plays an important role in shale gas adsorption, desorption and diffusion. Therefore, it is necessary to characterize the molecular structure of kerogen. In this study, four kerogen samples were isolated from the organic-rich shale of the Longmaxi Formation. Raman spectroscopy was used to determine the maturity of these kerogen samples. Highresolution transmission electron microscopy (HRTEM), 13 C nuclear magnetic resonance ( 13 C NMR) , X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were conducted to characterize the molecular structure of the shale samples. The results demonstrate that VR eqv of these kerogen samples vary from 2.3% to 2.8%, suggesting that all the kerogen samples are in the dry gas window. The macromolecular carbon skeleton of the Longmaxi Formation kerogen is mainly aromatic (f a '=0.56). In addition, the aromatic structural units are mainly composed of naphthalene (23%), anthracene (23%) and phenanthrene (29%). However, the aliphatic structure of the kerogen macromolecules is relatively low (f al * +f al H =0.08), which is presumed to be distributed in the form of methyl and short aliphatic chains at the edge of the aromatic units. The oxygen-containing functional groups in the macromolecules are mainly present in the form of carbonyl groups (f a c =0.23) and hydroxyl groups or ether groups (f al O =0.13). The crystallite structural parameters of kerogen, including the stacking height (L c =22.84 Å), average lateral size (L a =29.29 Å) and interlayer spacing (d 002 =3.43 Å), are close to the aromatic structural parameters of anthracite or overmature kerogen. High-resolution transmission electron microscopy reveals that the aromatic structure is well oriented, and more than 65% of the diffractive aromatic layers are concentrated in the main direction. Due to the continuous deep burial, the longer aliphatic chains and oxygen-containing functional groups in the kerogen are substantially depleted. However, the ductility and stacking degree of the aromatic structure increases during thermal evolution. This study provides quantitative information on the molecular structure of kerogen samples based on multiple research methods, which may contribute to an improved understanding of the organic pores in black shale.

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Effect of ocean oxidation on the chemical structure of marine kerogen

Cited by 16 publications

References 64 publications

Evaluation of Spatial Alignment of Kerogen in Shale Using High-Resolution Transmission Electron Microscopy, Raman Spectroscopy, and Fourier Transform Infrared

Evaluation of Spatial Alignment of Kerogen in Shale Using High-Resolution Transmission Electron Microscopy, Raman Spectroscopy, and Fourier Transform Infrared

Ferrate(VI) pretreatment before disinfection: An effective approach to controlling unsaturated and aromatic halo-disinfection byproducts in chlorinated and chloraminated drinking waters

Molecular Structure of Kerogen in the Longmaxi Shale: Insights from Solid State NMR, FT‐IR, XRD and HRTEM

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